1. Field of the Invention
This invention relates to reusable cartridge means for extracting precious metals from a solution containing such metal by means of a replacement reaction and, more specifically, it relates to such cartridge means which provide improved flow characteristics and ready access to the cartridge interior.
2. Description of the Prior Art
It is often desirable to recover precious metals from solutions containing such metals. For example, silver may be recovered from certain photographic solutions such as fixer solutions.
It is known that recovery of precious metals from a solution can be achieved by utilizing a replacement reaction. A replacement reaction occurs when a solution containing a precious metal is placed into contact with a replacement metal which is higher in the electromotive force series. The resulting chemical reaction causes the precious metal to be reduced and come out of solution and be recoverable either as a precipitate or as a plating on the replacement metal.
A number of devices and methods have been used in the past to place the solution in contact with the replacement metal. The method which is generally believed to provide the most complete replacement reaction is batch processing in which powdered replacement metal is placed directly into the solution and agitated. That method, however, is time consuming and considerable technical skill is required to determine the approximate silver or other precious metal content of the solution in order to ascertain the proper amount of replacement metal which must be added.
It has been known to employ continuous flow methods which pass a solution over a matrix of replacement metal, such as steel wool, metal gratings or even cylindrical rolls of window screening contained within a housing. Those methods while more convenient to use than batch processing often do not provide a complete reaction because there is either not sufficient surface area of replacement metal to contact all of the solution or because the solution develops passageways through the matrix which allow the solution to avoid contact with the replacement metal.
Another known continuous flow device utilizes metal powder dispersed on a porous inert medium such as alumina. Although the powdered metal initially presents a large surface area for a high reaction rate while deriving its support structure from the alumina, clogging frequently occurs as use continues and sometimes causes the solution to develop passageways through the structure which allow the solution to bypass contact with the metal.
In my earlier U.S. Pat. No. 4,325,732, I provide a solution to the above-mentioned clogging problem by employing a cartridge having inlet and outlet means and a spirally rolled exchange mass positioned therebetween. The exchange mass may be a flexible, resilient, fibrous material forming a self-supporting matrix which is non-reactive to the solutions with which it is intended to be used and has finely divided particles of replacement metal dispersed within the mass. As the exchange mass is capable of flexing, clogging within the mass is resisted. Although my earlier patented cartridge provides an effective metal recovery system, refinements thereto for providing even better performance would be desirable.